1. Field of the Invention
This invention relates to integrated circuits and in particular to such circuits wherein a glass film with a smooth surface is provided on the integrated circuit over the interconnect structure on the integrated circuit. This invention is particularly useful when the interconnect structure is aluminum or an alloy of aluminum but can also be used advantageously with other interconnect materials such as polycrystalline silicon ("polysilicon") selectively doped to a desired conductivity, or a polysilicide.
2. Description of the Prior Art
The use of glass films overlying aluminum interconnections on integrated circuits is well known. Unfortunately, because prior art glass films flow at a temperature significantly above that of the aluminum, once such a glass film is formed, the topography of the surface of the glass film is permanently fixed. Accordingly, should it be desired to smooth the glass flim to allow a second level of interconnects to be formed over the glass film, the underlying aluminum melts. To avoid or reduce this problem, first level interconnects are often formed of some material other than aluminum selected to have a melting temperature above the flow temperature of the insulating glass formed over the interconnect leads. This often raises the impedance of the interconnects and slows the circuit.